multiplexing
From Stumpr:
Details:
Multiplexing sends data from multiple clients to a single tape drive.
This is useful for low end clients with slow throughput (such as over a slow network connection). Since these clients cannot send data fast enough to keep the tape drive busy, multiplexing will allow backups of multiple clients to send data to a single tape drive simultaneously. Multiplexing is the process of alternately sending (interleaving) data. In this case, alternately writing or interleaving multiple clients data to a single tape.Multistreaming sends data from a single client to multiple tape drives.
Multistreaming is on the other end of the spectrum where there is a high-end client and throughput that is greater than a tape drive can handle. Multistreaming allows multiple backups (streams) of a single client to occur simultaneously to multiple tape drives.Multiplexing and multistreaming can be used together. The right combination can reduce backup times of large clients. Be aware that multiplexing will reduce the performance of restores. The larger the multiplexing factor, the greater the impact on restore performance.
Care should be taken to ensure that more than one stream does not access one physical disk at the same time, as this can cause "disk head thrashing" and may eventually lead to disk failure.
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Multistreaming can and should be used on ANY platform where you are experiencing extremely large filesystems. It is far better to backup smaller images than 1 huge image. Think about a 500GB server which is not that uncommon. If you can set up multistreaming to do 5 streams at 100GB in each stream then you can cut down the time by 1/5 the time to complete the backup. If one stream fails than this smaller 100GB stream is all that needs to be rerun. Meanwhile the other 400GB from the 4 streams that were successfull will not have to be rerun.
Multiplexing helps to keep the tape drive continuosly writing data and overall speeds up the backup time. it also helps prevent wear and tear on the tape drive heads as shoe-shining is minimized and sometimes eliminated if you can get a good enough amount of data pumped to the tape drives.
Thanks,
Karthikeyan Sundaram.
